1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and two shields.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a main pole that produces a magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write heads of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as an overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erase). To increase the recording density, it is required to prevent the occurrence of adjacent track erase.
Providing one or more shields near the main pole is effective for preventing the aforementioned skew-induced adjacent track erase and increasing the recording density. For example, U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1 describe a magnetic head including four shields: one having an end face located in the medium facing surface at a position forward of an end face of the main pole along the direction of travel of the recording medium; another having an end face located in the medium facing surface at a position backward of the end face of the main pole along the direction of travel of the recording medium; and the other two having two end faces located in the medium facing surface at positions on opposite sides of the end face of the main pole in the track width direction. The end faces of the four shields are arranged to wrap around the end face of the main pole in the medium facing surface.
In a magnetic head, a position forward of the main pole along the direction of travel of the recording medium is a position on the air-outflow-end side (the trailing end side), while a position backward of the main pole along the direction of travel of the recording medium is a position on the air-inflow-end side (the leading end side). Hereinafter, a shield having an end face located forward of the end face of the main pole along the direction of travel of the recording medium will be referred to as a trailing shield, while a shield having an end face located backward of the end face of the main pole along the direction of travel of the recording medium will be referred to as a leading shield.
In a magnetic head having one or more shields, there is typically provided a magnetic layer for connecting the one or more shields to a part of the main pole away from the medium facing surface. The one or more shields and the aforementioned magnetic layer function to capture a magnetic flux that is produced from the end face of the main pole and that expands in directions other than the direction perpendicular to the plane of the recording medium, and to thereby prevent the magnetic flux from reaching the recording medium. The one or more shields and the aforementioned magnetic layer also function to allow a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. Thus, the magnetic head having one or more shields allows prevention of the adjacent track erase and allows a further improvement in recording density.
The position of an end of a record bit to be recorded on the recording medium depends on the position of an end of the end face of the main pole located in the medium facing surface, the end being located forward along the direction of travel of the recording medium. For this reason, in the magnetic head having the leading shield and the trailing shield, it is important especially for the trailing shield to be capable of capturing as much magnetic flux as possible in order to accurately define the position of the end of the record bit.
In addition, as the frequency of the recording signal is increased in order to increase the recording density, the magnetic head is required to be improved in the rate of change in the direction of the magnetic flux produced from the end face of the main pole. To satisfy this requirement, it is particularly effective for the magnetic head having the leading shield and the trailing shield to shorten the length of a magnetic path that passes through the main pole and the trailing shield which captures much magnetic flux.
However, no attempts have been made to reduce the length of the magnetic path that passes through the main pole and the trailing shield.